Machines such as excavators, loaders, dozers, motor graders, and other types of heavy equipment use multiple actuators supplied with hydraulic fluid from a pump on the machine to accomplish a variety of tasks. These actuators are typically velocity controlled based on an actuation position of an operator input device. For example, an operator input device such as a joystick, a pedal, or another suitable operator input device may be movable to generate a signal indicative of a desired velocity of an associated hydraulic actuator. When an operator moves the input device, the operator expects the hydraulic actuator to move at an associated predetermined velocity.
In some situations, it may be possible for a pressure of the fluid supplied to one of the actuators to exceed a desired level. These over-pressure situations can occur, for example, when a first actuator becomes heavily loaded, forcing a greater portion of the system's fluid through a second uncompensated actuator at an elevated pressure. In these situations, the second actuator can be caused to overspeed, making the second actuator difficult to control and/or damaging the second actuator.
One attempt to synchronize the respective speeds of two actuators is disclosed in U.S. Pat. No. 7,059,125 of Oka et al. that issued on Jun. 13, 2006 (the '125 patent). The '125 patent provides a hydraulic controller that regulates the discharge flow rates from two different pumps to the two actuators, such that a difference in discharge flow rates between the pumps is reduced when the difference exceeds a threshold value. In this manner, control of the two actuators may be more predictable and stable.
Although the hydraulic controller of the '125 patent may help in the synchronizing of the speeds of two different actuators on a machine, it may be less than optimal. In particular, overspeeding of a first actuator may still occur when a second actuator being supplied by a separate pump becomes heavily loaded and a disproportionate amount of the total system flow gets sent to the first actuator.
The disclosed hydraulic control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.